The present invention relates to a transmission for cars and also how such a transmission is disposed in an advantageous manner in relation to the vehicle""s driving wheels.
It is a generally known trend that more and more car manufacturers are abandoning rear-wheel drive and instead are electing to have front-wheel drive and/or four-wheel drive. There are many advantages in having front-wheel drive compared with rear-wheel drive. One of them is that no propeller shaft or rear wheel transmission is required, creating extra room for passenger space and luggage space. One disadvantage of front-wheel drive is that the front wheel transmission on the one hand in the form of the gearbox itself, and on the other in the form of the final gear between the gearbox and the axle shafts, needs space and that this space requirement is directly adjacent to the engine. This can cause difficulties, particularly in connection with larger transverse engines, as the space for the gearbox is limited by the car""s track width, steering deflection etc. if it is to be positioned conventionally at one end of the crankshaft.
A gearbox is previously known from WO-9713990 which is intended to solve the aforementioned problems due to the fact that the gearbox is fitted with two parallel secondary shafts, which results in a considerable shortening of the construction length of the gearbox compared with a conventional design. However, a solution of this kind means that only the rotation of one of the secondary shafts performs usefull work at a time, while the other secondary shaft rotates in a void at an unfavourable gear ratio. It is thus unavoidable that such a solution causes certain energy losses. From the installation point of view also, a gearbox of this kind is disadvantageous in that the length of one axle shaft is limited, which can cause the axle joints to have to work in an unfavourable deflection range to provide sufficient wheel suspension play of the driving wheels.
Furthermore, the final gear in itself causes a problem in that it cannot be positioned according to the conventional art coaxially with the secondary shaft of the gearbox, resulting in difficulties in connection with any ambition to be able to construct compact gearboxes. A further problem with the conventional art is that it is not possible without major interference to change the gear ratio in an existing transmission, and often is virtually impossible to change before the primary shaft. Finally, it is the case that conventional gearboxes are difficult to fit with a controlled differential mechanism.
Another problem facing car manufacturers today is that cars which are built on the same sort of chassis are offered with a number of engine alternatives, The speed interval normally lies within varying ranges for different engine alternatives, making it difficult to use the same gearboxes. The problem is accentuated most when both diesel and petrol engines are offered, as a diesel engine has its power optimum at a speed which is considerably lower than a petrol engine, meaning that the petrol engine""s gearbox with optimal gear reduction is under-dimensioned for the diesel engine.
Finally, it is advantageous if a gearbox together with the engine forms a common preferably compact, assembly unit, in order to be able to optimise the unit from the assembly point of view.
The object of the present invention is to eliminate or at least reduce some of the aforementioned problems, which is achieved by means of a transmission for cars, preferably with driving of the front wheels, comprising an engine, a gearbox, a final gear, first link mechanisms which connect each axle shaft to said final gear, second link mechanisms which connect the other end of each of said axle shafts to their driving wheel and preferably an intermediate transmission between the engine and the gearbox, characterized in that said final gear comprises two planetary gears which give an exchange gear reduction of between 1.2:1 and 10:1.
By means of the solution according to the invention, the great advantage is achieved that the gearbox with final gear forms a mare compact and installation-friendly unit which results in the fact that it can be fitted transversely between the driving wheels and at the same time can obtain sufficient space for axle shafts with link mechanisms, which allow the necessary wheel suspension play of the driving wheels at the same time as it can be positioned to one side of the engine instead of at one end of it as according to the conventional art. This means that the engine design is not restricted to the same extent by restrictions on construction length, so that it can be constructed with greater freedom. It is certainly previously known in itself to have planetary gears for operating heavier vehicles, these being mounted directly on the driving wheel or close to it with a view to providing a further large gear reduction of the speed and in most cases also to reduce the load on the axle shaft. Thus a different problem to the present invention and for a quite different purpose, and not a comparable solution either.
According to a further aspect of the invention, a manual gearbox is used and the exchange gear reduction is either adapted in an intermediate transmission and/or in the planetary gear to the engine""s optimum speed range, so that the same kind of primary shaft and gear and the same kind of secondary shaft and gear can be used in the optimum manner for several kinds of engine with different kinds of speed range However, it is best if the same planetary gear is used which inter alia facilitates more rational production, adaptation being performed in the intermediate transmission which can be disposed in a very easily accessible and easily replaceable manner
According to further aspects according to the invention, it holds good that;
said planetary gears provide an exchange gear reduction of at least 2:1, and more preferably approx. 3-5:1.
said link mechanisms consist of conventional axle joints.
the secondary shaft is disposed parallel to at least one imaginary plane which either comprises the fulcrum for both driving wheels or the horizontal plane of the chassis.
the secondary shaft is disposed parallel to both aforementioned planes.
said planetary gear comprises a planet holder, a ring wheel and a sun wheel, and gear wheels supported on the planet holder, one of the planet holder, ring wheel or sun wheel being fixedly connected to, or fixed rotatably on, another fixed part forming part of the car, preferably the gearbox casing, while a second part is connected to the secondary shaft and a third part is connected to an axle shaft.
the length of an axle shaft with link mechanism is between 100-1000 mm, preferably between 200-700 mm (the distance between the hinge centre of the link mechanisms 16, 18 being intended)
the ring wheel is disposed fixedly or rotatably on the casing.
the gearbox is fitted in an engine compartment together with a transverse engine.
there is also a backwardly disposed transmission from the gearbox, the exchange gear reduction for the backwardly outgoing transmission corresponding to the exchange gear reduction from the planetary gear to the forward axle shaft, so that four-wheel drive can be obtained with the same speed at the front and back wheels.
a differential lock or controlled differential mechanism is disposed on the gearbox in interaction with said planetary gears, preferably via the ring wheel.
the exchange gear ratio in the intermediate transmission and/or the planetary gear is adapted to the optimum speed range of the engine, so that the same kind of primary shaft and gear and the same kind of secondary shaft and gear can be used in the optimum manner for several kinds of engines with different kinds of speed ranges.
the gearbox comprises a primary shaft with input gear and a secondary shaft with output gear.
said secondary shaft is disposed transverse to the longitudinal direction of the vehicle and placed in an area between the driving wheels.
the planetary gears are disposed coaxially in relation to said secondary shaft.